This invention relates to a process for recovering zwitterionic diazonium salts, derived from aromatic amines, which comprises: (a) diazotizing said amine to a zwitterionic diazonium salt in the presence of a cationic surfactant or (b) diazotizing said amine and thereafter treating the resulting zwitterionic diazonium salt with a cationic surfactant. The presence of the cationic surfactant during or after diazotization causes the zwitterionic aromatic diazonium salt to aggregate so as to give particles thereof which are readily separable from the liquid mass in which they are formed.
Amines can be diazotized by the use of several techniques. In the direct diazotization process, an acidic slurry of the amine is prepared and a nitrite is added thereto. In the so-called reverse method, the amine is dissolved in alkali, a soluble nitrite is added, and that mixture is poured into an acid, such as hydrochloric acid, so as to effect the diazotization. Various difficulties have been encountered with both methods. For example, in the diazotization of an aminosulfonic acid by the direct method, incomplete diazotization is often encountered if the aminosulfonic acid is not freshly precipitated in a finely divided state. While the reverse method usually results in complete diazotization of an aminosulfonic acid, the resulting insoluble zwitterionic diazonium salt is often formed in such a finely divided state that it is difficult to isolate. The process of the present invention provides for complete diazotization and results in the diazonium salt being in such a state of aggregation that it is readily separable from the liquid components in which it is formed.
In U.S. Pat. No. 2,845,326, a stable dispersion of a diazotizable primary amine devoid of solubilizing groups e.g. OH or SO.sub.3 H, is obtained by the combined use of a cationic compound and non-ionic compound.
In U.S. Pat. No. 2,812,321, it is disclosed that the addition of a surface-active agent of the polyoxyethylene fatty ester class to the 1,2,4-acid diazotization reaction mixture causes it to remain fluid throughout the diazotization process.
U.K. Patent Specification No. 1,072,702 discloses a process for producing a pigment having improved flow properties, dispersibility or gloss retention properties which comprises precipitating the pigment in the presence of two surfactants, or after-treating a slurry of the pigment with two surfactants, one of the surfactants being cationic and the other surfactant being anionic in character, and both surfactants having a surface tension of not more than 38.5 dynes per cm in a 0.2% by weight aqueous solution at 25.degree. C.